Semiautomatic telephone system



y 1932- T. s. SKILLMAN 1,859,476

SEMIAUTOMATIC TELEPHONE SYSTEM Filed Oct. 15, 1950 4 Sheets-Sheet 1 FIG.

SPECIAL smwc: OPERATOR sruc'ron OFF/CE A E E i $7."... E

l INVENTOR 5 rs, SKILL/VAN ATTORNEY com/5cm? May 24, 1932.

T. s. SKILLMAN SEMIAUTOMATIC TELEPHONE SYSTEM Filed Oct. 15. 1950 4 Sheets-Sheet 2 INVENTOR 7: 5. SK/L L AJAN A TTQRNE) 8 1932- T. s. SKILLMAN 1,859,476

SEMIAUTOMATIC TELEPHONE SYSTEM Filed Oct. 15. 1950 4 Sheets-Sheet 3 ATTORNEY Patented May 24, 1932 UNI ED STATE P m THOMAS SAMUEL SKILLMLAN, F ALDWYCH, LONDON, GLAND, ASSIGN'OR TO WESTERN ELECTRIC COMIBAN Y, INCORPORATED,

A ooRroRArron or nEW YORK SEMIAUTOMA'IIC TELEPHONE SYSTEM Application filed October 15, 1930, Serial mfisasvi, and in Great Britain February 12, 1930.

This invention relates to telephone exchange systems and more particularly to such systemsin which toll connections are established between central offices by means of machine switching equipment controlled over toll lines. The objects of the invention are to provide improved methods and means for enabling an operator at one office toextend a connection over a toll line to a subscribers station in a distant office through the use of automatic switching mechanism controlled by alternating current impulses, preferably within the voice frequency range; to provide the operator with means, likewise controlled by alternating current impulses preferably within the voice frequency range, for complete supervision over such a connection and also to provide suitable circuit arrangements in a system of this nature whereby traflic may be handled in either direction over the same toll line. More specifically, the invention contemplates an improved arrangement of a two-way toll line which can be switched at either end to the local machine switching equipment in response to a signal from the other end so that a call maybe set up inone direction by means of a plurality of coded voice frequency impulses designating the wanted number and transmitted over said line into a registering and controlling mechanism at the terminating ofiice, while a call in the opposite direction may be set up by a plurality of alternating current impulses of a single frequency produced by the operation of a dialing device at an operators position and transmitted over said line for to operating automatic switches connected the trunk line at the distant end.

While the establishment and control of telephone connections on a two-way basis over a toll line is old in the telephone art it is believed that the relatively simple and inexpensive equipment and cooperating circuits disclosed in the present invention furnishes an eflicient and reliable means forestablishing two-way toll connections between subscribers over toll lines.

In accordance with the invention, therefore disclosed herein by way of illustration this one specific embodiment of which isis accomplished in the following improved. manner: y

The .toll trunk line terminates in a jack at an operators position in each of the two of-. fices which are connected by the said toll line and at each of which positions there is the usual positional equipment such as interconnecting cords, V operators telephone circuit and other apparatus well known to the art. At each end the trunk is also extended to a switching relay'which responds to a connection from the distant end andserves to switch the trunk conductors from the operators position'at the incoming end to the automatic switches or to a registering and controlling mechanism which, when operated in the known manner, extend the toll line to the wanted subscriber. At each end of the trunk there is also provided a number of tuned alternating current relays connected in parallel across both sides of the trunk through a repeating coil and each responding to a single voice frequency current circuit. These relays, in turn, control a group of lo; cal directcurrentrelays which, whenoperated in response to a corresponding operation of the voice frequency relay or combinanism, said mechanism thereafter causes the" operation of'the said-automatic 'switches'in the known. manner to extend the toll' line connection to the wanted subscribers line.

The operators position at one end of-the cause the operation or release 7 trunk terminus which, for the sake, of convenience is designated herein as oflice A, is provldedwlth a key-set containing ten none locking keys, each of which keys designates one of the ten digits. Thesekeys are suitably wired to four separate sources of voice frequency currents, either separately or n,

combination, at each key. Common to all the tion with a common position key and circuits combinations controlled by the cord inserted into the trunk jack, as more fully explained hereinafter, connects to the trunk line the voice frequency circuits controlled by the digit key depressed;

g The voice frequency current sources which are wired to the key-set arelikewise extended to a separate group of relays, independent of the key-set, to effect the transmission'to the other end of the trunk for a call established in the opposite direction, of other voice frequency impulses the component frequencies of each of which correspond to a distinct supervisory signal to be transmitted to the originating end of the trunk line so that a supervisory signal is transmitted on a voice frequency impulse basis to the originating endof the trunk and there, by the voice frequency responsive relays responsive thereto, the impulse is translated to the correspondingly standard supervisory signal well known in the art.

The operators position at the other end of the trunk terminus which, for'the-sake of convenience is herein designated as oflice B, is'provided with a dialing device capable, when connected to the line in the well known manner, of producing line interruptions or impulses. These. impulses, in combination with-a dialing key at the position where the trunk terminates in office B, control local direct current circuits which effect the intermittent closure of a single voice frequency circuit to the trunk line. At office A, each voice frequency impulse causes the operation of the voice frequency relay which is tuned to respond to the voice frequency'current of the impulse. A direct current relay responds to the operation of the voice frequency relay and, in combination with the operation of an other direct current relay, causes the translation of the impulse into the'familiar'twowire direct current impulse, which may be transmitted into the automatic switches connected to the trunk. The automatic switches respond to each translated impulse and extend the toll connectionto the wanted'subscribers line. The trunk line at officeB likewise contains local circuits controlling the closure of voice frequency current sources in requisite for the transmission to ofiice A of the various supervisory signals originating at ofiice B for effective recognition at oflice A in a call extending from oflice A to I In general, the system operates in the following way: u I wishes to extend a connection to a wanted subscriber in thedistant oflice B she takes into fuse the toll trunk connecting the two ofiices by inserting into the trunk jack at her position' atoll cord whichisarranged in the. well known manner. Sh'e thereafter depresses the i the relays and direct current When an operator at oflice A heard, and she will proceed thereafter to complete the call. I

Before she proceeds with the function of depressing the keys designating the wanted number, however, she waits for a signal that the trunk is ready to receivethe impulses to be produced by the successive operationof the various digit keys. This signal, in the present embodiment of the'invention, takes lamp and is the result of sending out from ofiice A an impulse of a combination of certain voice frequency currents which effects the response of voice frequency relaysat oflice B. This impulse at oiiice B causes the opera tion of the trunk switching relay thereat, connects the trunk conductors to thelocal auto:

matic switches, establishes a busy tone circuit for the operator at ofiice B and causes the connection of a register and control mecha nism to the direct current circuits controlled by: the voice frequency responding relays. Thereafter, a return impulse is transmitted form of lighting the toll cord supervisory back to oflice A which results in lighting'thesupervisory lamp in the cord, thereby indieating to the operator at oflice A that the trunk is ready for key sending. The operator depresses the common position key and proceeds thereafter to depress in definite succession the digit keys representing the number of the called subscriber. With each key depressed a coded voice frequency impulse is transmitted over the line for a definite duration. These key impulscscause the response of voice frequency relaysat oflice B which are tuned to operate on the separate voice frequency currents of which the impulse is composed and, by their operation, effect the op -f V eration or release ofrdirect currentrelays which translate the received impulse into a regular two-wlre direct current impulse as already mentioned. The automatic switches are then set in the well known manner and the called subscr ber is rung. l/Vhen the sub scriber answers, a supervisory relay inthe toll trunk, connected in a loop clrcuit with the subscribers line 1s operated and its operation controls a local circuit which closes onto the trunk line a voice frequency circuit of a definitercombination of voice frequency ,cur-' rents. The appropriate voice frequency relays at oflice A respond to this impulse and,

in turn, control local direct current circuits which extinguish the supervisory lamp in the operators cord circuit as an indication that thesubscriber has answered. Whenzthecall terminated, the release of the supervisory circuits located at the understanding of the invention.

end of the trunk, the effectof which'is to light the supervisory lamp in the cord circuit as an indication to the operator that the call is over and to remove the toll cord from the trunk. V

Ifa call is to be extended from ofiice B to oficeA the operator at ofiice B proceeds in a similar manner to take the trunk into use and likewise makes the busy test by listening for a busy tone. The designation of the called number in this case, however, is not transmitted by the depressionof keys and the consequent transmission of coded impulses composed of voice frequency currents but, rather, by the operation of a dialing device E which is in series with a local relay whose contacts control a group of relays oneofwhich intermittently closes an alternating current source of a single voice frequency to the trunk. V

This voice frequency circuit is closed as many on its .way to normal. The resulting voice frequency impulses cause the operation of the corresponding voice frequency relay at office A whose operation controls local circuits which aifect u c a relay in the automatic switch connected to the trunk line so that a called subscribers line at oflice A is reached by direct currentimpulses in the well known manner. The operation of the supervisory signals are, in general, controlled in the same way as those for 36 a connection extending from office A to oflice B as already described.

A clearer conception of the scope and purpose of the invention may be obtained by consideration of the following description taken in connection with the attached drawings in which:

' Fig. 1 shows a part of the apparatus and circuits located at one end of the trunk line .connecting with an operators position and Y the machine switching selectors.

Fig. 2 shows the remaining apparatus and circuits located at the same end.

F ig. 3 shows a part of the apparatus and distant end of said trunk line.

Fig. 4 shows the remaining parts of the apparatus and circuits at said distant end connecting with the operators position and local automatic switches and control mechanism.

Fig. 5 shows the order in which the above mentioned drawings are to be arranged with respect to each other in order to obtain a clear the present embodiment of Uircm'z operation with calzs from ofice A v to 077506 B i will consider first the extension of calls in one direction, sayfrom office A, indicated crates at this time and also, in

by the'circuits shown in Figs. 1 and 2, to oflice B, indicated by the circuits shown in Figs.- 3 and 4. The operator, at whose position in office A the trunk terminates in jack 114, upon receiving an order for a wanted all of the windings of relays 209 and 215 and the same battery is connected in parallel by way of conductor 239 to the winding of relays 220 and 222; Relay 222 operates by a ground closure on the other side of its winding through the right back contacts of relay 221. Relay 220, however, does not operate from the ground on the back contacts of relay. 209, due to the fact that, when the above mentioned resistance battery was extended to'the windings of relays 209 and 215, a circuit was closed for relay 209 from the above mentioned battery through resistance 244, No. 1 winding of relay 209 to ground on the back contacts of relay 205 and also overl'another circuit through its No. 3 winding to ground on the back contacts of relay 207. Relay 209 operates,'opens its contacts and prevents the operation of relay 220 at this time. Likewise, relay 215 operates from the same battery in parallel over a circuit through its N o. 3 winding to ground on the back'contacts of relay 206 and also through another circuit over its N o. 1 winding to ground on the back contacts of relay 204. On its right inner contacts, relay 210 closes a circuit for slowto-operate relay 221 by way of the back contacts of relay 213, normally made contacts of relay 208, left outer contacts of relay 227, winding of relay 221 to battery. Relay 221, however, is sufficiently slow in operating so as to allow relay 222 to erate before the ground on its back contacts is removed. The ground at the right contacts of relay 210 is also extended through the top outer contacts of relay 213 to the winding of slow-to-operate relay 225 which also opthrough the right outer contacts of relay 225,

to the right winding of relay 216 causing thisrelay to operate and look over its left windtop inner.

parallel fully op ing and left inner contacts to ground on the contacts of relay 215. I The operation of relay 216 closes, at its left outer contacts, a loop including coil 211, the tip and ring conductors of the cord circuit and a relay in-the cord circuit through the back contacts of which is controlled the circuit of the cord supervisory lamp. relay operates in this circuit and extinguishes the supervisory lamp. At-its left middle con- The cord supervisory tacts relay 216 closes a circ from battery th 219, left'm ground on the which relay is norma Nos. 1 and 2 windings contacts of relays 204C Relay219 operates but performs no use The operating path of through the already mentione seized at the distant o the opposite direction, efiective, as more fully once the trunk has A and relay 210 oper erates over the above gfrom ground on the co d, on its left inner closes one step of the circuit quency current source Z winding P of repeating 0 closing step. being contr right outer cont operate ondary connected relay 240 whose a outgoing trunk conductors Relay 221, w above, closes a circui right. front contacts which relay, it will b release, winding of relay ing relay 224 erates relay 2 the operation 0 operation of relay 2 V on its right contacts contacts of relay 225 to t 228. \Vhen relay 224: operate cuit for relay 2 10 ner contacts, wind VWhen relay 2 10 op lineconductors 233 and 23 winding S of repeating coi ts right inner c nding P of re windin 210 an also closes 1 side ofthe primary coil 229, placing source in paral current source Z, w the same side of the prima repeating coil 229 by contactsof relay 224. said primary win permanently conn turn circuit C of a sources. consisting of comb is impressed over through the secondary 229 and transmitted ove ductors 233 and 234 to The: durationo iddle contacts front contac lly operated over its circuits of voice'frequency sources W and to ground on the back to the primary winding of the repeating coil. and 205 respectively. The calling impulse circuit above described is e above circuit traced through conductors 233 and 23 1, top ful function at this time. and bottom back contacts of relay 300, top v relay 213 is controlled and bottom primary windings P and P of acts of relay 210, as repeating coil 301 through both left windings I if the trunk is in series of repeating coil 316. The impulse B for a call in is repeated through both secondary windings.

front cont winding S of re to the normally open rmatures are conne 233 and 23 1. ted as d crib d open the circuit of winding No. 4 of relay 312. p

d on its Now relay 312 is normally operated by the contacts of relay 222, circuits over the two windings mentioned e remembered, is slow above and will, therefore, release when these 224 t batt y, a gcircu ts are opened, but relay 311, which is Relay 221 alsooplikewise normally operated, remains oper- 26 ver an obvious circuit and ated CV61 its NO. 2 winding t0 ground On the f this latter relay a e th back contacts of relay 307. The releaserof j 28 by extending ground relay 312 closes a ground on its left contacts, th hth i ht inner right winding of relay 315 to battery, causes h wi di f r l y relay 315 to operate thereby and, on'its'right it closes a i contacts, relay 312'closes ground on conductor d on it l ft i 330, top winding of relay 400 to battery. Reingof relay 240 to battery. lay 400 operates over this circuit. Relay hen opera t from groun from groun this impulse is uit for relay 219 by the releasing time of slow-to-release relay: rough the winding of relay 222 whose circuit is opened by the operation of relay 216 to of relay 221. The release of relay 222 causes ts of relay 237, the release of relay 22 1, in turn cutting off the 70 it will no longer be S and S of repeating coll 301 over a circuit described hereinafter, including the said secondary windings and,

lugged into at office voice frequency responding relays 302,303, ated. Relay 225 op- 304t'and 305 connected in parallel between traced circuit to its both of the said secondary windings in series. ntacts of relay This calling impulse operates relays 302 and acts, 305, the former responding to voice frequency .from voice 'fre- W and the latter to voice frequency Z. V The to the primary operation of relay 302'opens the short circuit 1 229; the final around the left winding of relay 306, causing lled through the this relay to operate over both of its winding lay22l when it is in series. The operation of relay 306 opens ibed hereinafter. The secthe normal circuits ofwinding No. 1 of relays .eating coil 229 is 311and 312 respectively. Likewise, the op contacts of eration of relay 305 removes the short circuit it to operate over both windings in series an grates it connects t k 315 closes battery through resistance 340 over 4 t th da y its left outer contacts conductor 34:1, to the 1 229. Belay 224C 7 windings of relay 310 and to the winding of ntagts t e relays 322, 323 and 327. As soon as this batti tery supply s available at the windings of ni frequency t. relays 310, 1t will operate in a circuit over lel with voice frequency lts No. 3 winding to ground on the back conhi h i l connected t tacts of relay 308 and through its No. 4: windi di P f ing to ground on the front contacts of relay f th ri ht t r 309, which relay is operated over the callinght id f th impulse circuit from oificeA. Relay 310, on

f th repeating 11 operating, closes circuit over its contact t d t th 160111111011 and left inner contacts of relay 315 to' the u vgice frequency current lOCkll'lg Of relay. GX- l. in' pulse th f tends the ground on its contactsover conduc: d f f i gyvi g, Z tor 331, bottom' No. 1 contacts and lower the primary P, repeated winding of relay 400 to battery thereby lock- S of repeating coil ing this relay. The operation of relay 400 r the trunk line conconnects a busy tone source BT over a path the distant office. B.- from one side of the secondary of said busy,

determined tone source BT,top No. i contacts-ofrelay 400,'conductor 418, of key 430 to the top contacts of key 428 and from the other side of the secondary of busy tone source BT, top No. 3 contacts of relay 400, conductor 419 to the bottom inner con tacts of key 428. When key 428 is operated for the purpose described hereinafter and relay 431 is operated thereby over an obvious circuit, this busy tone circuit is completed over the above mentioned contacts of key 428, condensers 426 and 432, contacts of relay 431 to the operators telephone circuit OT which is not shown. When, therefore, the operator at ofiice B desires to take the trunk into use for extending a connection in the opposite direction to oflice A and this trunk has already been appropriated by the operator at oflice A to extend a connection to office B, the operator at office B, in order to ascertain whether or not the trunk is busy, operates key 4280f the trunk. The operation of the key operates relay 431 and connects the operators telephone circuit OT to the busy tone source T over the a'fore-traced circuit. The busy tone circuit will be applied in the well known manner to the operators receiver and indicates to her that the trunk is busy. If, on the other hand, the trunk is idle at the time that the operator at office B makes the busy test by operating key 428, relay 400 will be normal, the busy tone circuit is not closed and the operator will receive no tone, indicating thereby that the trunk is free and available. I

Relay 400, on operating, switches the trunk conductors 342 and 343 over the top and bottom No. 2 front contacts to conductors 424 and 425, respectively, connecting with the local automatic selector indicated schematicallyin Fig. 4.

When the calling impulse above described is terminated relays 222, 224, 226,227 and 240 release at office A and relays 302 and 305 release at office B, in turn short-circuiting the left windings of relays 306 and 309, respectively, causing these latter relays to release. Relay 312 re-energizes over its No. land N o. 4 windings due to the release of-relays 306 and 309, and ground is connected to conductor 414by way of the left front contacts of relay 312, conductor 332, bottom No. 3 contacts of relay 400, right contacts of relay 412 to conductor 414. This ground is for the purposeof initiating the operation of the register and control mechanism connected or con trolled over this conductor in order that the said mechanism becomes connected to the calling trunk and local selector. The register and control mechanism above mentioned is neither shown nor described herein as it forms no part of the present invention and the connection between the calling trunk, the local switching selector and the control mechanism may be brought about in any suitable manner.

normally made contacts tery. Relay When the register and control mechanism" is ready for operation as a result of the initial grognd on conductor 414, a ground is received ground is passed through the right inner contacts of this relay, conductor 433, tothe left winding of relay 326. Relay 411 is made slow to operate and relay 326 slow to release so as to give relay 326 sufficient time to operate before'its energizing circuit is cut oif at the contacts of relay. 411 by the operation of this latterrelay, and relay 326 is prevented from releasing immediately when this circuit is opened due to its slow releasing qualities. Relay 411, at its left inner contacts, locks over its left winding to ground on conductor 331 and, at its left outer contacts, closes a circuit for relay 404 from ground on conductor 414 thereby causing relay 404 to operate and'close through conductors 334, 335,336 and 337 to the mechanism connected tothe contact banks to which the other side of these are extended. Relay 326 closes a circuit for relay 324 from ground on the left back contacts of relay 329, left contacts of relay 326, winding of'relay 324,tresistance 317 to bat- 324 energizes and, at its left contacts, closes the circuits from voice frequency current sources, W and Y, conductor 333, to the primary winding P of repeating oil 320, the other side' of which primary winding is permanently connected to the common return 0 of the voice frequency sources. Relay 324 also closes'an obvious circuit from its right inner contacts to the top winding of relay 300, causing this relay to operate andswitch the trunk conductors 233 and 234 to the secondary winding of repeating coil 320. As soon as the voice frequency circuits W and Y are'closed, an impulse of these combined frequencies is, there fore, sent out over the trunkto ofl'ice A. This impulse circuit is traced from thesecondary winding S of repeating coil 320, top and bottom front contacts of relay 300, conductors 233 and 234, top and contacts of relay 240, top'and bottom primary windings P and P of repeating coil 232, top middle back contacts and bottom No. 2- back contacts of relay 213, condensers 245- and 246, winding of relay 212 and condenser 247 which close the trunk loop. This impulse is repeated over a circuit including the secondary windings S and S5 of repeating coil 232 and voice frequency relays 200, 201, 202 and 203 connected in parallel betweenboth of said secondary wind-'- ings. The impulse energizesvoice frequency relays 200 and 202. Relay 200 opens register and control conductors on conductor 413 which will operate relay 411 over its right winding and the same bottom back its contacts, removing the short circuit around the right winding of relay 204 and causes this relay to operate over both its windings in series, while relay 202: in' a simitermination of the above presses lar-manner, causes theoperation of relay 206. The operation of relays 204 and 206 opens the energizing circuits of relay 215 through itsNos. land 3 windings, respectively, and causes it to release. The release of relay 215 unlocks relay 216 which, it will be recalled, had energized over the right outer back contacts of relay 225 when the trunk was first plugged into at office A and locked to the contacts of relay 215. The release of relay 216 opens an aforetraced loop to the cord circuit, releases the supervisory relay therein and causes thereby the lighting of the cord supervisory lamp. This indicates to the operator at office A that the trunk is ready for the transmission of key impulses. At the described impulse from ofiice B, relays 200 and 202 release causing, in turn, the release of relays 204 and 206 and the consequent reoperation of relay 215.

The operator, to perform this function, de-

and thereafter depressesin succession the digit keys of key-set 119 in the order corresponding to the wanted number at office B. Each depression of the key sends animpulse of voice frequency current over the trunk. The duration of each impulse, however, is not regulated by the length of time the operator keeps the digit key depressed but by the operating time of relays 118 and 117. Whenever a digit key is depressed, say for example,

trunk,

' di it key 3, a circuit is closed from ground on conductor 120, right contacts of key 3, winding of relay 118 to battery. Relay 118 opcrates and, on its right outer contacts, closes an obvious circuit for slow-operate relay 117 and, on its left contacts and through the outer contacts of relay 117 closes one side of the primary winding of repeating coil 116 to conductor 102 of the voice-frequency sources common return circuit, whilethe other side of the primary of repeating coil 116 is closed over the right inner contacts of relay 118 and inner contacts of relay 117 to the left contacts of the individual keys of key-set 119. Relay 117, however, is slow to operate and its time characteristics may be regulated in the well known manner to suit the desired duration of the impulse. When it operates, after a time interval, the impulse current is cut off, even though the operator may still have key 3 depressed. The duration of the impulse, therefore, is regulated by the operating time of relay 117 no matter how long the digit key is kept down. Now the voice frequency code for the digit 3 impulse is WX so that a circuit from these two separate voice frequency sources is closed over conductors 101 and 103 to the left contacts of key 3 and from thence through the right contacts of relay 118, inner contacts of relay 117, primary winding of repeating coil- 116, outer contacts of relay 117 left contacts of relay 118 to the return completing circuit on' conductor 102.

key 100, which is individual to the This combination of voice frequency currents is then repeated in the secondary windings of the repeating coil 116, the circuit being carried through the contacts of key 100, top middleback contacts and bottom No. 2 back contacts of relay 213, trunk conductors 230 and 231, primary windings P and P of repeat ing coil 232, back contacts of relay 240, trunk conductors 233' and 234, back contacts of relay. 300, primary windings P and P "of repeating coil 301, left windings of repeating coil 316. The impulse is then repeated through the secondary windings S and S of repeating coil 301 to the voice frequency relays 302, 303, 304 and 305. The impulse consisting of voice frequency currents W and X causes the operation of relays 302 and 303.

It will be noted that the voice frequency relays 200, 201, 202 and 203 at office A are connected to the secondary windings S1 and S of repeatingcoil 232, through the primary windings of which passes the impulse current above described, Although the impulse is repeated through secondary windings S and S of repeating coil 301- at office B, causing thereby the response of the proper voice frequency'relays, a

similar repetition of the impulse current into the secondary windings" flow of current through these windings and the voice frequency relays connected between them, On the other hand, the secondary windings S and S of the repeating coil301 at office B are connected to the high potential s de of the line with respect to an incoming signal and, consequently, the impulse current divides between the primary winding P and the associated secondary winding S so that.

the current through the sec'ondary 'winding of repeating coil 232 at'oflice A canhas an aiding effect, thereby increasing the induced voltage between; the two secondary windings and the corresponding flow of cur-' rent through these windings and the voice frequency relays connected between them. It

is thus seen that for a key impulse transmitted from office A to oiiice B the impulse current is differential with respect to the secondary windings of the repeating coil on the near side of the line'and aiding with respect tothe secondary windings of the repeating coil on the far side of the line. Although key impulses are not transmitted in the opposite direction when establishing a call from office B to office A as described hereinafter, an inspec- 302 and 303 tion of the drawings will make it clear that the same thing would be true with respect to an impulse in such a direction if it should be thought advisable to modify the present embodiment of the invention to send key impulses in both directions.

The operation of relays 302 and 303 causes the operation of direct current relays 306 and 307 in the described manner. Relay 306 connects ground to conductor 334 and effects thereby the closure of a circuit in the register and control mechanism of that component of the impulse as is represented by voice frequency current W. In a like manner relay 307 grounds conductor 335 to register in the control mechanism that component'of the impulse as is represented by voice frequency current X.

It will be observed that the operation of relays 306 and 307 does not result in a disturbance of the circuits controlled by relays 310, 311 and 312 due to the fact that, in some cases, the holding circuits of these relays are not disturbedwhile in others, although the holding circuits are open, yet the relays are sufliciently slow in releasing so as to hold up during the impulse intervals between the successive depression of digit keys at office A. When the impulse is terminated relays release, in turn releasing relays 306 and 307 and removing ground from conductors 334 and 335. Each succeeding impulse resulting from the depression of any of the individual keys ofkey-set 119 results in the operation of one or more relays 302, 303, 304 and 305 with a corresponding grounding of one or more of the conductors 334, 335, 336 and 337 for the registration of the various components of the transmitted impulses in the register and control mechanism. WVhen all of the thus transmitted and recorded, the automatic equipment functions in the well known man ner to extend the line through to the called subscribers line in the local automatic on cc and to cause his bell to be rung. When the called subscriber answers, battery is con nected by the selector switch to conductor 424, top N o. 2', front contacts of relay 400, conductor 342, winding 318 of repeating coil 316, conductor 338, winding of relay 403 to ground. Relay 403 operates and,- inturn, operates slow-release relay 402. Relay 402, at its right outer contacts, closes ground to operate slow-operate relay 329 by way of conductor 435, normally made contacts of relay 313, right outer contacts of relay 324, Winding of relay 329 to battery; Before relay 329 operates, however, relay 402 has closed a circuit from battery through resistance 436, conductor 339, to the windingof slow-re lease relay 327 which relay Operates to ground on the left back contacts of relay 329 before this relay operates. hen relay 329 operates, a circuit is closed for relay 325 from impulses have been and causes the lighting battery through the winding of relay 325, contacts of relay 327 left front contacts of relay 329. Relay 325 operates and closes an obvious circuit for relay 300 over its top winding. Relay 325 also closes through the circuits from voice frequency sources WV and X to the primary winding P of repeating coil 320 so that an impulse of combination voice frequency current VVX is transmitted over the trunk by way of trunk conductors 233 and 234 to ofiice A over the trunk loop previously traced. Since relay 329 in energizingalso opens the circuit of relay 327, the releasing time of this relay determines the duration of the impulsetransmitted. This impulse causes the operation of relays 200 and 201 at office A and relay 237, which is normally energized over windings 1 and 2'is caused to release by the operation of relays 200 and 201 andthe resulting operation of relays 204 and 205. Relay 237, by releasing, ops erates relay 216 over its right winding, which relay locks over its left winding and left inner contacts to ground on the front contacts of relay 215. Relay 216, over its left outer contacts, closes an aforementioned loop to the cord circuit through the retardation coil 211 and thereby causes the eXtin'guislr' ing of the supervisory lamp in the cord C11:

cuit as an indication that the subscriber has answered, which signal is maintained as long as the conversation continues as no circuit exists to unlock relays 2 15 and 216, theformer relay holding over its No. 1 and 3 windings to'ground on the back contacts of relay 204 and 206 at the termination of the answering impulse. I

At the conclusion of the conversatlon the called subscriber restores his receiver, open ing thereby the'subscribers loop and causing the release of relays 403, 402 and 329. Relay 329 on closing its back contacts operates relay through resistance 317, winding 324, left contacts of relay 326, which relay is slow release andwas operated over itsright winding to ground on the left front contacts of relay 329, back contacts of relay 329 to ground, so that an impulse. of the .combination voice frequency WY is transmitted over the trunk during the time that relay 324 is operated. When relay 326 'releases,'relay 324 likewise 324 over a circuit from battery releases and the impulse is terminated. Since relay 400 is still energized, relay 328 is ineffective in prolonging this impulse beyond the time controlled by the release of relay 326. At oflice A this impulse causes the operation of relays 200 and 202, thereby operating relays 204 lay 215 which, in turn,

releases relay 216. Relay 2l6'opens the loop to the cord circuit of the supervisory signal therein. At the and 3 windings from ground on the back conand 206 and releasing re- 125 termination of the impulse relay 215 reoperates over its No. '1

' relay 225 opens the circuit of relay 228. Both of these relays are slow release and, during the interval in which'they are held in an operated position, a circuit is closed to energize relay 227 from ground on the back con- 15 tacts of relay 221, left contacts of relay 226 or right contacts of relay 228, winding of relay 227 to battery. Relay 227 will thus operate and remain operated until relays 226 and 228have released, each of whose separate circuits depends on the release of relays 221 and 225 respectively. The circuit of relay 221 is opened as soon as relay 227 breaks'its left back contacts and that of relay 225 on the releasing of relay 210 which, as already pointed out,"releases assoon as the operator withdraws the plug from the trunk jack. Relay 227 operates relay 240 over an obvious circuit and also closes the circuit from voice frequency sources W and Y to the primary winding P of repeating coil 229. An impulse of current of these two frequencies is now transmitted over the trunk to oflice B in the described manner and causes thereat the operation of relays 302 and 304. The

' operation ofthese relays-operates relays 306 and 308 and they, in turn, release relay 310. Relay 310 releases relays 315, 411, 412 and 400. Relay 315 releases relay 327. The circuits of relays 310, 323 opened by the release of relay 315 so that only relays 311 and 312 remain normally energized at the termination of the impulse and thus restore the trunk to normal.

7 If the called and will alternately operate and release relay 403 which, in turn, will alternately operate and release relay 402. Relay 402 will alternately operate and release relay 329 and relay 329 will alternately operate and release relay 327 over a circuit'from ground on the left back contacts of relay 329, winding of I relay 327, to battery through resistance 340 on-the left outer contacts of relay 315, which relay remains locked to the contacts of relay 310 if the release signal as above described is not transmitted from office A as it would not be in the case when the subscriber does not answer. Relay 327 operates relay 325 'from ground on the left front contacts of relay 329, contacts of relay 327, winding of relay 325 to battery, and the same ground on the left front contacts of relay 329 is extended'in a parallel circuit to the right wind- The release of and 322 are likewise subscriber is found busy, a busy flash signal will be received over the automatic selectors by way .of conductor 424 and release simultaneously with relay 327. 7

Relay 326, on its left contacts, closes a circuit from battery v winding of. relay 324, left contacts" of relay 326 to ground on the left back contacts of relay 329. Consequently when relay 329 releases, relay 326, being slow release, the above traced circuit for relay 324 becomes effective thereby causing this relay to operate. Thus it is seen that relay 325 operates when relay 329 is operated and relay 324 operates when relay 329 is released. This causes alternate combination circuits'to sources and WY respectively to be closed and the corresponding impulses transmitted over the. trunk. The impulse WXoperates relays 200 and 201 at office A causing the corresponding operation of relays 204' and 205 respectively. Relay 204, at its back contacts, opens the circuit to the No. 1 winding of relay 237, and relay 205, at its back contacts, opens the No. 2 winding of this relay. Relay 237 releases and, at its back contacts, closes an aforetraced circuit to the right winding of relay 216 which, when operated, locks over its left winding and left inner contacts to ground on the contacts of relay 215, which latter relay remains operated over its No. .3 winding from the back contacts of relay 206 and battery through resistance 244 on the left contacts of. relay 210. Relay 216'cl0ses, on its left outer contacts, the loop including coil 211 to the cord circuit, operating the supervisory relay therein and extinguishing thereby the cord-supervisory signal. f

Then the impulse consisting of frequencies WX has terminated and that of frequencies WY immediately follows, relay 200 remains operated but relay 201 releases and relay 202 operates. In consequence relay 205 releases and relay 206 operates. The operationofrelay 206 opens the remainingoperating circuit over the No.3 windings of relay 215 causing this relay to release and open the locking circuit of relay 216 which relay thereafter releases. Relay 216 at its left outer con-- tacts opens the aforementioned loop to the cord, releases the supervisory relay therein and thereby causing the relighting of the supervisory signal. Thus the alternate trans mission of voice frequency impulses l VX and WY, when the called subscriber is busy, causes the flashing of the supervisory lamp in the cord circuit at ofiice A as an indication of this fact. 7

If, when the called subscriber is busy, the operator at office A wishes to offer the call to the operator at the distant oflice B, she may doso by ringing over the trunk. The ringing equipment is so arranged that a voice manual position and from which point the call is then completed in the well known manthrough resistance 317, I

ner.- The ringing current is applied from the cord circuit in the well known manner and energizes relay 212 which, in turn, energizes relay 223 over an obvious circuit. Relay 223 closes the circuits of voice frequencysources XZ on the trunk line. At offi'ce 303 and 305 are operated by the voice frequency combination and they, in turn, operate relays 307 and 309 to open the circuits to the Nos. 2 and 4 windings of relay 314 thereby causing it to release. Relay 314 operates relay,410 over an obvious circuit which locks over its right contacts to ground on conductor 331 to the contacts of relay 310. Relay 410 closes ground on its left front contacts to conductor 415 which leads to a special service operators position. The auxiliary operator then extends the call in the well known manner; supervision being received back by wa of conductors 416, 424 and relay 403. When the call is terminated and the called subscriber restores, the restoration of the trunk to its normal position takes place in the manner already described.

Uz'rom't operation with calls from ojfice B to When the operator at the outgoing position of office B inserts the plug of the calling cord into trunk jack 405, relay 406 operates from a battery circuit extending from the sleeve of the cord, sleeve of jack 405, winding of relay 406 to ground. The operation of relay 406 closes a circuit for relay 403 from ground through the winding of relay 403, conductor 338, winding 318 of repeating coil 316, conductor 342, top N o. 2 back contacts of relay 400, normally made contacts of key 430, winding 421 of repeating coil 422, contacts of relay 406, winding of retard tery. Relay 403 operates and, in turn, operates relay 402. A previouslydescribed circuit is now closed for relay 329 from ground on the right outer contacts of relay 402, causing this relay to operate. The operation of relay 402 likewise closes, on its right inner contacts an aforetraced circuit from batterythrough resistance 436 to lay 327 which operates back contacts of relay 329 before this relay has broken its back contacts. When relay 329 operates, a previously described circuit through the contacts of relay 327 is closed for relay 325 and this relay now closes, on its right contacts,the circuit to the top winding of relay 300. It also closes on its left contacts the circuits from the voice frequency sources W and X to the primary P of the repeating coil 320. A voice frequency impulse of the combination WX is now transmitted over the trunk line in the manner already described in connection with the establishment of a call in the opposite direction to the one now under consideration.

At oflice A this impulse causes the operthe winding of re- B relays coil 429 to bat-;

from round onthe' ation of relays 200 and 201, the operation of relays 204 and 205, the consequent release of relay 237 and the operation of relay 216in the manner described. When relay 216 operates it closes battery through resistance 241 on its right inner contacts to all the windings of relays209 and 215 and'to the windings of relays 220 and 222. Relay 209-'oper,-' ates over its N o. 3 winding to ground onthe back contacts of relay 207 and relay 215 operates over its No. 3 winding to the back contacts of relays 206'and N o. 2 winding to the front contacts of relay 205. The operation of relay 215 closes'a locking circuit for relay 216 from ground on its front contacts, left inner contacts of relay 216, left winding, to battery. Relay 222 also operates from ground, on the right back contacts of relay At the end of the impulse, relay 237" to the trunk conductors 235 and 236 sotha t, endeavors to time, a circuit can be if the operator at oflice A seize the trunk at this completed over the trunk conductors through the cord to her telephone circuit substantially in the same manner as already described for operator B that the trunk is in use.

way of the top middle front 2 front contacts to the conductors 217. and 218 connecting with the two windings 112 and 111 respectively of repeating coil 121 andthe local switching the automatic repeaterof selectors. Relay 219, over its right'contac'ts,

closes a circuit for relay 105 in the automatic repeater from battery through the winding of relay 105, conductor 115, left outer contacts of relay 225, right back contacts of relay 220, right contactsof relay 219 to ground on the back contacts of relay 204. Relay 219 also connects battery through resistance 242 and left contacts to the windings of relay" 238 which, however, does-not operate at this time. Relay 105, on its left contacts, closes" relay 104 which operan obvious circuit for ates and, on its right contacts, closes the mug conductor 125 preparatory to the receipt of the repeated dial impulses as described here inafter. Belay 104 connects; ground to con ductor 122 and to one ing of relay 110.

Since the automatic equipmentat'office battery: left middle contacts of to apprise her of the fact Relay 213 also switches the trunk conductors 230 an'd'231 by and bottom No.

side of the right windso that as soon as 'the trunk is arranged conductors are switched to-the automatic selectors no further delay is necessary to wait the attachment of a recording mechanism for; the reception of dial impulses, need for supplying the operator-at oflice B with dial signal as was the case in the extension of a call in the opposite direction from ofiice A tooiiice B, where a register and control mechanism has to be connected to the trunk before the incoming impulses can bestored. The operator at oflice B does not waitfor a dial signal after the trunk has been seized and has made a busy test therefor'but proceeds to dial the wanted number without any further delay. 1

The operator atoffice B prepares to dial operating dialing key 430 and thereafter tion of key 430 transfers the first impulse,

i riod. .Neither does'relay 300.

1 left contacts and at operating the dialing device 408. The operav I the circuit of relay 403 from battery through coil 429 to battery through the contacts of the dialing device 408 and resistance 409. On the return of the dial, relay 403 releases for each impulse and, on closes a circuit from ground on its back contacts,bottom No. 4 contacts of relay 400, conductor 437, windings of relay 322 and 323 in parallel, left outer contacts of relay 315, resistance 340 to battery. The

3 ground side of'this circuit also extends from the windings of relays 322 and 323 to the bottom winding of relay 300. Relays 322, 323 and 300 operate. Relay 322 is slow to release and does not release during the impulsing pe- R'elay 323, however, operates for each break period of the dial and closes through the circuit of voicefrequency W to theprimary winding P ofrepeating coil 320. At the distant end,this causesthe operation of relays 200 and 204 in the described manner. The operation of relay 204 opens the afore-traced operating circuit of relay 1050f the automatic repeater, the circu'itreelosing again at the end of the 5. impulse. Relay on closing its left back contacts closes a ground through the left contacts of slow-releasing relay 104 to the winding of relay 106. Relay 106 operates, short-circuits the trunk conductors at its its right contacts closes a circuit for relay 107 from ground on the right contacts of relay 104, which locks to operating ground; Relay 107,-in turn, closes a circuit for relay 109 which operates, but performs no function at this time. As the im pulses are transmitted, relay 105 alternately releases-and operates,-thereby opening and closing-the'trunk loop-conductors to the automatic-selector,=caus1ng it to step in the known L manner and connect to another. selector of thersuccessive switching stage or to the final connector. Thus for each impulse produced by the dial 408 there-corresponds an impulse for relay 105. In this way the successive operation and release of relay 105 .causes the there is no proper setting of the automatic equipment connected to the repeater shown in Fig. 1 in the -well known manner.

When the pulsing is terminated and the called subscribers lineisxreached, relay 105 reoperates, relay 106 releases and both windings of relay 110, .inzseries with relay 108, are

on the right contactsof-re-lay 104.

When the called subscriber answers relay 110 is operated'over the above-traced loo-p andthis relay closes groundon its contacts,

conductor .127, left back-contacts of relay 220, conductor 243, top inner front-contacts of relay 213, normally made contacts of relay 208, left back contacts of'relay 227, winding of relay 221 to battery. Relay 221 operates and, at its right front' contacts, closes a circuit for relays 224 and .226. Relay :224 operates under the control of relay 222 and which, in turn, hasits circuit-opened when relay 221 operates. Relay 226 operates z-but performs no useful function at this time. Since relay 225 is now not energized, relay 224 sends out an impulse consisting of voice frequency combination and "not 'RVZ, thereby causing the operation of relays 302 and 303 and the consequent release "of-relay 311-at'office B in the described-manner, QR-elay 1311 operates relay 31 5 overits rightwi'nding and this .latterrelay closes a circuit from battery through retard coil 321,ri ght"contacts of relay 315, winding 31:9'of'repeating coil 316, conductor 343, bottom No. :2 c'ontacts of relay 400, trunk conductor 4*19,winding 423' of repeating-coil422, winding-of relay 407 toground. The-'operationof relay 407 establishes a loop overthe"cord"in'=series withsupervisory relay therein which operates and extinguishes the supervisory lamp in the cord circuit as anindicationthat the called subscriberhas-answered.

At the conclusion of thecal lxthe subscriber at office A restores his receiver, thereby releasing relay 110 which on opening its contacts,releases-relay relay 227 byway of the lleft conta'cts'o f relay .226, thereby causing "the closure and transmission of :a "voice frequency impulse WY tooflice B. Relays 302, 304,306,"and 308 operate as :a result of this impulse, thereby opening 1 the circuit ,of relay 310 which ';then releases. Belay 315 now releases and opens, the circuit of relay 407, causingithereby the lighting of the supervisory l-l'amp inthe cord 124 of repeating coil 121., right. winding of relay 11:0,conductor'122 to ground 221. ddelay 221 operates circuit as an indication to the operator that the call is terminated and that she may remove the cord from the trunk. VVhc-n the cord is removed, relays 403 and 402 release, thereby releasing relays 329, 322, 310 and 327. Relay 329 operates relay 324 in the described manner through the left contacts of relay 326 and closes voice frequency combination lVY to ofiice A. The duration of this impulse is governed by relays 324, 328, and 326 as previously described. The impulse WY causes the operation of relays 200, 202, 204 and 206 at ollice A with the consequent release of relay 215 and the unlocking of relay 216 as well as the release of relays 222, and 213, thereby restoring the trunk b normal at office A.

If the subscriber is found to be busy, a busy flash is transmitted over the subscribers loop to supervisory relay 110 which, on op erating, intermittently operates relay 221 over the afore-traced circuit. Relay 221 will, by the successive operation and release of relays 224 and 227 in the described manner transmit back over the trunk voice frequency impulses lVX and VVY alternately. Impulse W X causes-the operation of relays 302 and 303, the operation of relays 306 and 307 the consequent rcleaseof relay 311 and the operation of relay 315. Relay 315 closes an aforetraced circuit for relay 407 whichextinguishes tie cord supervisory signal as already described. Impulse WY causes the operation of relays 302 and 304, the operationot relays 306 and 303, the release of relay 310, the release of relay 315, the consequent release of relay 407 and the lighting of the cord supervisory lamp as already de scribed. Thus relay 315, by operating and releasing in response to the two voice fre quency signals, operates and releases relay 407 and, in turn, flashes the cord supervisory lamp in accordance with the busy signal.

Orcm't seized at both ends If the trunk circuit is seized at both ends,

then the insertion of a cord in trunk jack 114' operation. of relay while the insertion at oi'lice A will. cause the 210 as already described of a cord in trunk 405 at ofice B will cause the operation of relay 216 as already described. Thus, a race will ake place between the operation of relay 210 and relay 216. If relay 210 should operate first and break its right back contacts, then the operation of relay 216 will not be effective for operating relay 213 since the operating circuit for this relay is controlled from ground on the right outer contacts of relay 216 and the right outer back contacts of relay 210. Under such circumstances a circuit is closed for relay 225 from ground on the right inner contacts of relay 210, top outer contacts of relay 213, winding of relay 225 to battery. A circuit is now closed for relay 221 from office B where the impulse causes the operation of relays 302 and 305 and the consequent release of relay 312 in the manner described. A circuit is now closed for relay 400 from battery through its top winding, conductor 330, to. ground on the right contacts of relay 312. The operation of relay 400 closes the circuit from busy tone -source BT transmitting busy tone to the operators telephone circuit to indicate to the operator at ohice B that the trunk has been taken into use at the other end. Relays 403 and 402 will have been operated, however, prior to the operation of relay 400 over a previously described circuit with coil 429 in series with relay 403. L his circuit, however, is interrupted by the operation of relay 400 thereby preventing the backward transmission or" an impulse of voicefrequency combination WY by the consequent energization of relay 324. This is prevented by relay 401 which short-circuits relay 324 over its front contacts for a time which is long enough to prevent relay 324 from sending a complete signal. This circuit is not effective when relay 411 is energized so that no interference will be occasioned when relays 403 and 402 release as a result of the subscriber restoring. If either opera-tor plugs in at any later stage of the call she will receive busy tone in the manner already described.

In case the operator at oflice A seizes the trunk on a connection established at oi'iice B and during the time that the release signal is being transmitted thereto, the insertion of the cord will not disturb the complete transmission of the release signal since the ground on the contacts of relay 210 cannot be effective to operate relay 221 until relay 227 has released, which latter relay, as previously noted, controls the duration and transmission of the release signal to ofice B. Likewise, in case the operator at ofiice B seizes the trunk for the establishment of another call when a connection already exists from a set-up in the opposite direction and during the time that a releasesigna-l is being transmitted to office A as a result of the release of relay 403, the insertion of the cord will not result ina shortening of the releasing impulse as the slow releasing characteristic of relay 401 maintains this relay operplug in jack 405 ated for the proper interval and, in turn, prevents the operation of relay 324 which is necessary for the transmission of the sapulse for preparing the distant end of'the trunk for the reception of dial impulses.

*lVihat is claimed is? 1, Ina telephone exchange system comprisin'guafirst and second telephone office, a .two-way trunk line interconnecting sail ofii'ces, a plurality of alternating current sources of different frequencies in each of said ofiices, means at said'first ofiice for selectively applying said plurality of alternating currentsources to said trunk line to produce coded alternating current impulses thereover, means -atsaid second office for applying one of said plurality of alternating current sources over said trunk line to produce al "ernating current impulses of a single frequency thereover, means responsive to the appropriation of said trunk line at said first cr'lice for setting up a connection at said second office by the said coded alternating current impulses, and means responsive to the appropriation of said trunk line at said second ofiice for setting up a connection at said first office by the said alternating current impulses V of a single frequency.

2. In a telephone exchange system comprising a first and second office, a two-way trunk line interconnecting said ofiices, a plurality of alternating current sources of dif ferent frequencies in each of said ofiices, means at said first ofiice for selectively apply ing said plurality of alternating current sources to said trunk line'to produce coded alternating impulses thereover, means at said second ofiice for applying one of said plurality of alternating current sources over said trunk line to produce alternating current impulses of a single frequency thereover, a register and controlling mechanism at said second ofiice means for connecting said register and controlling mechanism to said trunk line, means-in said trunk line at said second office responsive to said coded alternating current impulses, and means controlled by said responsive means for transmitting said impulses to said register and controlling mechanism.

3. A telephone exchange system comprising afirst and second .office, a two-way trunk line interconnecting said oifices, a plurality of alternating current sources of different frequencies in each of said ofi'ices, means in said first office for selectively applying said plurality of alternating current sources to said trunk line to'produce coded alternating current impulses thereover, means at said second office for applying one of said plurality of alternatingcurrent sources to said.

trunk line to produce alternating current impulses of a slngle frequency thereover, a register and controlhng mechanism at said second office, means for connecting said regissources of different frequencies sponsiveto said coded alternating current impulses for transmitting said impulses to said register and controlling mechanism when a connection is extended in one direction,' and means in said trunk line at said first office responsive to alternating current impulses of a single frequency for operating said'automatic switches when a connection is extended in the opposite direction.

4:. A telephone exchange system comprising two telephone offices and a two-Way interconnecting trunk line with means for extending a connection in one direction by coded alternating current voice frequency impulses transmitted thereover and for extending a connection in the opposite direction by alternating current impulses of a single frequency transmitted thereover, and means responsive to the appropriation of said trunk line at one of said ofiices for rendering said trunk busy at the other said oifices until the said means are restored to normal.

5. In a telephone exchange system comprising a first and second ofiice, a two-way interconnecting line between said first and second oflices with means for extending a connection in one direction by coded alternating current voice frequency impulses transmitted thereover and for extending a connection in the opposite direction by alternating current impulses of a single frequency transmitted thereover, a first relay device responsive to the appropriation of said trunk line at said first ofiice for controlling further means for extending a connection to said second ofiice,

a second relay device responsive to the appropriation of said trunk line at said second office for controlling further means for extending a call in the opposite direction to said first office, means responsive to said first relay device to render said second relay device ineifective to extend a call to said first office, and means responsive to said second relay device to render said first relay device ineffective to extend a call to said second office. Y

6. In a telephone exchange system comprising a first and second ofiice, a two-way trunk line interconnecting said two offices and terminating in each of them at an operators position, automatic switches in each of said ofiices, a plurality of alternating current in each of said offices, means in said first ofiice for selectively applying said plurality of alternating current sources over said trunk line to produce a plurality of coded alternating current impulses thereover, means at said second oifice for selectively applying said plurality of alternating current sources to produce a plurality of coded alternating current impulses thereover, means at said second oflice for applying one of said plurality of said alternating current sources oversaid trunk line to producealternating current impulses of a single frequency thereover, means at said first ofiice responsive to one of said coded impulses transmitted from said second office for disconnecting said trunk line from said operators position at said first office and extending it to said automatic switches when extending a connection from said second ofiice to said first ofiice, meansresponsive to said impulses of single voice frequency transmitted from said second office for operating said automaticswitches, means at said sec ond ofiice responsive to one of said coded impulses transmitted from said first oflice when extending a connection from said first ofiice to said second office for disconnecting said trunk line from said operators position at said second oflice and extending it to said automatic switches, and means responsive to other coded voice frequency impulses transmitted from said first ofiice for controlling the operation of said automatic switches in said second office. r

7. In a telephone exchange system comprising a first and second office, a two-way trunk line interconnecting said two oflices and terminating in each of them at an operators position, cord circuits and operators telephone circuits at each of said operators positions, automatic switches in each of said ofiices, a plurality of alternating current sources of different frequencies in each of said olfices, means in said first office for selectively applying said plurality of alternating current sources over said trunk line to produce a plurality of coded alternating current impulses thereover, means at said second office for selectively applyingsaid plurality of alternating current sources over said trunk line to produce a plurality of coded alternating current impulses thereover, means at said second oifice for applying one of said plurality of alternating current sources over said trunk line to produce alternating current impulses of a singlefrequency thereover, means at said first office responsive to one of said coded impulses transmitted from said second office when extending a connection from said second ofiice to said first ofiice for disconnecting said trunk line from said operators position at said first office, for connecting said trunk line to said automatic switches at said first office, and to connect busy tone to said operators telephone circuit at said position-at said first ofiice, and means at said second office responsive to one of said coded impulses transmitted from said first office when extending a connection from said first office to said second office for disconnecting said trunk line from said operators position at said second ofiice, for conbusy tone to said operators telephone circuit V at said-second'office.

8. In a telephone exchange'syst'eml com- 1 prising two offices, an interconnecting twoway line between said offices, automatlc switches, register and controlling mechanism"- at one of said offices and automatic switches at the other of said ofiices all capable of operable association with the respective end of said trunk line in response to the appropriation of said trunk line for theextension of a call from the other end'of said line, an impulsing device at each ofi'ice capable of being operably associated with each end of said line, sources of alternatingjcurrent of different frequencies in each of; said offices, means controlled by said impulsing device in one of said offices for selectively effecting cir cuit closure between saidsources of alternating current and said line to produce coded alternating current impulses thereover, means controlledby said vice in other of said ofiices 'foreifectlng a circuit closure between one of said sources of alternating current and said trunk line-1 to produce alternating current'impulsesof a single frequency over said trunk line, a plurality of tuned alternating current relays operably associated with said trunk line at each end thereof, each 'of saidalternatingcurrent relays being responsive to an alternating current of a particular frequency, a plurality of direct current relays controlled by said tuned alternating current relays, means controlled by said direct current relays at one of said oflices and responsive to the operation of said tuned alternating current relays by said coded alternating current impulses for transmitting a corresponding direct current impulse to said register and 'controllingdevice, and means controlled by saiddirect current relays at other of said oflices and respon sive to the operation of one of said-tuned alternating current relays by said alternating current impulse of a single frequency for producing a direct current impulse to control said automatic switches in said first'office.

9. In a telephone exchangesystem comprising two offices, an interconnecting twoway trunk between said offices, automatic switches and register and controlling mechanism at one of said ofiices and automatic switches at other of said oflices all capable of operable association with the'respective end of said trunk line in response to the appropriation of said of a call from the other endof said line, an impulsing device at each of said oflices capa-' ble ofbeing operably associated with'e'ach end of said line, sources of alternating current of different frequencies at'each end of said oifices, means controlled by said'impulsother impulsing de'- trunk line for theextensiona repeating coil at each end of said line,-each of said repeating coils having a plurality of primary windings and a plurality of secondary windings and each of them operably associating said alternating current relays to said trunkzline ateach end thereof, each of said repeating coils being adapted to increase the sensitivity of said relays at one end tocurrents coming from the opposite end of said line, and todccrease the sensitivity of said relaysatone end to current coming from the same end of said'line, a plurality of direct current relays controlled by said tuned alternating current relays, means controlled by said direct currentrelays at one of said offices for transmitting adirect current impulse to said register and controlling device when said alternating current relays respond to a coded alternating current impulse and means controlled by-said direct current relays at saidother oflice for producing a direct current impulse to control said automatic switches whenone of said tuned alternating currentrelaysrespond to one of said alternating current impulses of a single frequency.

10. Ina telephone exchange system comprising two ofiices, an interconnecting two wa line between the said offices, automatic switches and register-and controlling mechanism at one of said oflices and automatic switches at the other of said offices all capable of operable association with the respective end of said trunk line in response to the appropriation of said trunk line for the extension of a call from the other end of said line, an impulsing device in each of said oflices capable of being operably associated with each end of said line, sources of alternating current of different frequencies at each of said offices, means controlled by said impulsing device in one of said oflices for selectively effecting the circuit closure be tween said sources of alternating current and said line to produce coded alternating current impulses there'over, means controlled by said other impulsingcdevice in the other of said oflices'for effecting a circuit. closure between one of] said sources of alternating current and said trunk line toproducealternating current impulses of a single frequency thereover, a plurality of tunedalternating wcurrent relays,leach of said relays'being 'responsive to an alternating current of a particular frequency, a repeating coil at each end of saidline, each of said repeating coils having a plurality of primary nected in series in said line and shunted by a resistance and a plurality of secondary windings, said secondary windings beingin shunt of said line through said alternating current relays to increase the sensitivity of said relays at one end of said line to currents coming from the opposite end of said line and to decrease the sensitivity of said relaysv at one end of said line to currents coming from the same end of said line, a plurality of direct current relays controlled by said tuned alternating current relays, means controlled by said direct current relays in one of said offices for transmitting a direct current impulse to said register and controlling device.

when said alternating current relays respond to acoded alternating current impulse, and means controlled by said direct current relaysat said other office for producing a direct current impulse to control said automatic switches when one of said tuned alternating current relaysresponds to one of said alternating current impulse of a single frequency.

11- In a telephone exchange system 'comprising a first oflice and a second'ofiic'e, a twoway trunk line extending between said offices, means including a cord circuit and automatic switches controlled by a series of coded alternating current voice frequency impulses transmitted over said trunk linefor establishing a connection between said two offices inone direction, means including acord and automatic switches controlled by a series of alternating current impulses'o-f a single voice frequency transmitted for establishing a connection between said two offices in the opposite direction, a'supervisory signal in each of said cord'circuits, a plurality of sources of alternating current of different frequencies in each of said offices, means for producing code impulses of different frequencies over said trunkidine, and

means responsive'to said code impulsesover said line to control said supervisory signal.

12. In a telephone exchange system comprising a first office and a second oflice, a twoway trunk line extending between said offices, means including a cord circuit and automatic switches controlled by a series of coded alternating current voice frequency impulses transmitted over said trunk line for establishing a connection between saidtwo oflices in one direction, means including a cord circuit and automatic switches controlled by a series of alternating current impulses of a single voice frequency transmitted over said trunk linefor establishing a connection'between said two offices in the oppositedirection, a supervisory signal in each of said cord circuits, a plurality of sources of alterwindings conover said trunk line nating current ofdifierent frequencies operably associable with said trunk line ateach end thereof, means for producing coded impulses of difierent frequencies at each end of said trunk lin'e depending upon the direction of the connection, each of said impulses being composed of a different voice frequency current combinations according to the condition which said impulse is to indicate, alternating current devices at each end of said trunk line responsive to said impulses and means at each end of said trunk line responsive to said alternating current devices for locally operating said supervisory signal in said cord circuit. 13. In a telephone exchange system comprising a first office and a second ofiicc, a two-way trunk line extending between said ofiices, means including a cord circuit and automatic switches controlled by a series of coded alternating current voice frequency impulses transmitted over said trunk line for establishinga connection between said oflices in onedirection, means including a cord circuit and automatic switches controlled by a series of alternating current impulses of a single frequency transmitted over said trunk line for establishing a connection between'said otfices in the other direction, a supervisory signal in each of said cord circuits, a plurality of sources of alternating current of different voice frequencies operably associable with said trunk line at each end thereof, means for transmitting impulses of different frequencies in either direction over said trunk line depending upon the direction of a connection, each of said impulses being composed of different voice frequency current combinations according to the condi tion which said impulse is toindicate, a plurality of tuned alternating current relays at each end of said line responsive to said impulses, and a plurality of direct current relays at each end of said trunk line responsive to the operation of said tuned alternating current relays for locally operating said supervisory signal insaid cord circuit.

14. A telephone exchange system comprising a first oflice and a second oflice, a twoway interconnecting trunk line extending between said ofiices, means including a cord circuit and automatic switches controlled by a series of alternating current voice frequency impulses ofva single frequency transmitted over said line for establishing a connection between said oflices in one direction meansincluding a cord circuit and automatic switches, mechanism, said automatic switches'and said controlling mechanism being controlled by a plurality of coded alternating current voice frequency impulses transmitted over said line, for establishing a connection between said otfices In the opposite direction, a supervisory signal ineach of said cord circuits,

and a register and controlling a plurality of alternating current sources of ifferent voicefrequencies operably associable with said trunk line at eachend thereof, means for tran mitting coded impulses .of different frequencies over said trunk line'in either direction, means responsive to the connection of said cord circuit to said trunk line at said first office for extending said trunk line to said register and controlling mechanism at said second oflice, and means responsive to the connection ofsaid trunk line to saidregister and recording mechanism for transmitting a coded alternating currentimpulse to the originating end: of said line for operating said supervisory signal in the cord circuit. a V

15. In a telephone exchange system comprising a first office and a second office, a two way trunk line extending between said offices, a called line-in each of said offices, means including a cord circuit and automatic switch-es controlled by a series of coded alternating current voice frequency impulses transmitted over said trunk line for establishing aconnection between said oflices in one direction, means including a cord circuit and automatic switches controlled by a series of alternating current impulses of a single frequency transmitted over said trunk line for establishing a connection between said oflices in the opposite direction; asuperisory signal in each of said cord circuits, a plurality of sources of alternating current of different frequencies operably associated with said trunk line at each end thereof, a relay device at each end of said trunk line responsive to each distinct condition of said trunk line, said automatic switches and said called line when interconnected for the extension of a connection from one office to said called line in the other office in the appropriate direction, and means controlled by said relay device for transmitting to the originating end of said trunk line an"alternating i current impulseof a frequency combination corresponding to any one of said distinct conditions of said trunk line, said automatic switches and said called line at the terminating end. i

16. In a telephone exchange systemcomprising a first oflice and a second ofiice a twoway trunk line extending between said offices, a called line in each of. said offices, means including a cord circuit and automatic switches controlled by a series of, coded alternating current voice frequency impulses transmitted over said trunk line for establishing a connection between said oflices in one direction, means including a cord circuit and automatic switches controlled bya series of alternating current impulses ofa'single frequency transmitted over said trunk line for establish ing a connection between said offices in the opposite direction, a supervisory signal in each of said cord circuits, a. plurality of (iii ' mati c switches and sources; of alternating current of different frequencies operably associable with said .trunlc'line' at each. end thereof, a relay device at'each end of said trunkresponsive: to eachidistiaict' condition of said trunk, said antomatic switches and said called line when interconnectedfor the extension of a connection from one ofiice: to said calledline in other oflice' in the appropriate direction, a relay, the circuit or said relay being prepared by said relay device when operated, and means controlled by saidrelay: when operated and said relay. device when released forv transmitting to the originating. end of said trunk an alter- 'nating: current impulse of a frequency C0l11+ bination corresponding to any one of said dist nct conditions of saidtrunlr, said autosaid called line at the terminating end;

17'. In a telephone exchange system COII1- prising a first office and a second ofiice, a twoway trunk line extending between said offices, a -calledline' in-each of said oiiices. means incl udinga cord circuit and automatic switches controlled by a series of coded alternating cnrr ent' voic efrequencyimpulses transmitted over said: trunk line for establishing a connection between said :two offices in one direction, meansincluding' a cord circuit and aritomatic switches controlled by a series of ale ternating: currentimpulses of asingle voice frequency transmitted over said. trunk line for" establishing a: connection between said ofiices-in the oppos te direction, a supervisory signal: in each of'saidcord circuits, a plurali-ty of: sources of alternating current of different frequencies operably associable with said trunk line at each end thereof, a re device at eachicndio-f' said trunk responsive to a plurality of distinct conditions of said trunk, said automatic switches and said called line when interconnected for the extension oat a connection from one oifice to said called line in theother ofiice in the appropriate directioma first relay and asecond: relay, the circuit of said first relay being prepared by said'relay device when operated and the circuit of said second relay being prepared by said relay device when released, means controlled by said first relay when operated for transmitting to the originating end of said trunk line an alternat ng current of a frequencycombination corresponding to one of said'distinct' conditions of said trunk, said autoinatic'switches and said called line at the termin-ating'end, and means controlled by said-second relay when operated for transm tting a current impulse of a different frequency combination corresponding to one of said distinct conditions of said trunk, said automatic switches and said called 'line at terminating end.

In a telephone exchange system comprising a firstioifice and a second ofiice, a twowaytrunk line extending between saidoiiices,

isseyrze means including a cord circuit and automatic switches controlled by a series of alternating current impulses 0t a'single frequency transmitted over said trunk line for establishing aconnection between said ofiices in the oppos te direction, a supervisory signalin each of said cord circuits, aplurality of sources of alternating currents of different frequencies operably associable with said trunk at each end thereof, a relay device at each end ofsaidtrunkresponsive to a plurality of distinct conditions of said trunk-said automatic switches and said called line when interconnect-ed for the extension of'a connection'from one ofiice to said called line in other oflice in the appropriate direction, a'slow release relay responsive to the release of said relay device, a first relay and a second relay, the circuit of said first and controlled through the contacts of said slow release relay, means controlled by said first relay when'operated for: transmitting to.- the originating end of said trunk line anal-ten natin-g current impulse b nation corresponding tinct' conditions of said trunk, said automatic switches and said called line at the terminating end, andmeans controlled said second rel aywhen operated for transmitting to the orig nating end of saidiline an alternating cl-irrent-impulse of a differentfrequency combination corresponding toone of said dis tinct' conditions of said trunk, said automatic switches and said called line at said term nating end.

In a telephone exchange system comprising a first and second ofiice, a two-way interconnecting trunk line between said ofiices terminating in each of them at an operators position, automatic switches in each of said offices, an'impulsing devlce, a key and cord circuit at each of said operatorspositions capable of operable association with said trunk line when said cord is connected to said trunk line, a relay at each end of said trunk, said automatic switches in each of said offices extending to contacts of each of said relays and means responsive to the operation of said key at one of said positions at one end of said trunk, for operating said relay at the second relays being of a frequency coinsto one of S21.1d-(1lS'-' distant end of saidtrunk for completing an impulsing circuit oversaid impulsingdevi'ce, said trunk and said automatic switches "at said distant end. i

20. In a telephone exchange system comprising a first andasecond office, a two-way interconnecting line between said offices and terminating in each of them at anoperators position, automatic switches in each of said 

